SQL log backup promoted to FULL every time in DB mirror configuration.

Hi All,

We are backing up SQL 2012 mirror system. We backup both nodes in cluster and backup configured with Virtual name.

We have SQL server configured in Cluster and running the backup with Virtula name.

Backup was working fine as FULL and LOG (INCR). now after configuring Mirror with this DB we start getting issue with LOG backup (INCR).

Every time I initiate LOG backup it does show INCR in NETWORKER console but takes full backup of the DB and logs not getting truncate.

I know with log shipping option I should face this kind of issue but not with Mirrioring configuration.

T Log shipping does include backup operation and brake the chain so in next incr backup it does FULL but it should not work like this in Mirrioring configuration.

Networker server 8.2.1

NMM version - 8.2.1 (Backup configured through SQL VDI)

it's not AOAG it's just a Database Mirroring.

So I have configured the backup with same user and credentials which is used for configure SQL DB mirror.

2 Prod server in cluster and 1 DR server which we are using to send the logs.

on all nods I am using same user and networker services started with the same user name and password.

FULL backup is working fine but when I initiate an INCR backup it promoted to full.

Following error message I am getting once the backup is completed.

8008:(pid 10364):One or more arguments are not correct.

29085:(pid 10364):Microsoft SQL Server Provider error:

38006:(pid 10364):SQL Server Network Interfaces: The target principal name is incorrect.

38006:(pid 10364):Cannot generate SSPI context.

66212:(pid 10364):Cannot login to SQL Server DRserver\DBname.

29085:(pid 10364):Microsoft SQL Server Provider error:

38006:(pid 10364):Invalid authorization specification.

66212:(pid 10364):Cannot login to SQL Server DRserver\DBname.

37786:(pid 10364):Unable to determine status of mirror partner backups for database 'DBname'.  Backup level forced to full.

Note: I am using the same user and password which is used for configuring DB Mirror.